Download ch 16 Evolution of Population 3

16-3 The Process of
Speciation
16-3 The Process of Speciation
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16-3 The Process of Speciation 16-3 The Process of Speciation
Natural selection and chance events can change the
relative frequencies of alleles in a population and
lead to speciation.
Speciation is the formation of new species.
A species is a group of organisms that breed with one
another and produce fertile offspring IN NATURE.
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16-3 The Process of Speciation
Isolating Mechanisms
The gene pools of two
populations must
become separated for
them to become new
species.
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16-3 The Process of Speciation
Isolating Mechanisms
Isolating Mechanisms
As new species evolve, populations
become reproductively isolated from each
other.
When the members of two populations cannot
interbreed and produce fertile offspring,
reproductive isolation has occurred.
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16-3 The Process of Speciation
Isolating Mechanisms
Reproductive isolation can develop in a variety of
ways, including:
• behavioral isolation
• geographic isolation
• temporal
/ seasonal isolation
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16-3 The Process of Speciation
Isolating Mechanisms
Behavioral Isolation
Behavioral isolation occurs when two populations
are capable of interbreeding but have differences
in courtship rituals or other reproductive strategies
that involve behavior.
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16-3 The Process of Speciation
Isolating Mechanisms
Geographic Isolation
Geographic isolation occurs
when two populations are
separated by geographic barriers
such as rivers or mountains.
Geographic barriers do not
guarantee the formation of new
species.
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16-3 The Process of Speciation
Isolating Mechanisms
Temporal Isolation
Temporal isolation or seasonal isolation occurs
when two or more species reproduce at different
times of the year.
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Speciation in Darwin's Finches
Speciation in the Galápagos finches
occurred by:
• founding of a new population
• geographic isolation
• changes in new population's gene pool
• reproductive isolation
• ecological competition
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Founders Arrive
A few finches—
species A—travel
from South
America to one of
the Galápagos
Islands.
There, they survive
and reproduce.
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Geographic Isolation
Some birds from
species A cross to
a second island.
The two
populations no
longer share a
gene pool.
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Changes in the Gene Pool
Seed sizes on the
second island
favor birds with
large beaks.
The population on
the second island
evolves into
population B, with
larger beaks.
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Reproductive Isolation
If population B birds cross back to the first island,
they will not mate with birds from population A.
Populations A and B have become separate
species.
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16-3 The Process of Speciation
Testing Natural Selection
in Nature
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Ecological Competition
As species A and B compete for available seeds
on the first island, they continue to evolve in a way
that increases the differences between them.
A new species—C—may evolve.
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16-3 The Process of Speciation
Testing Natural Selection
in Nature
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16-3 The Process of Speciation
Speciation in Darwin's Finches
Continued Evolution
This process of isolation, genetic change, and
reproductive isolation probably repeated itself often
across the entire Galápagos island chain.
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16-3 The Process of Speciation
Studying Evolution Since
Darwin
Studying Evolution Since Darwin
Scientific evidence supports the theory that living
species descended with modification from common
ancestors that lived in the ancient past.
Scientists predict that as new fossils are found,
they will continue to expand our understanding of
how species evolved.
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16-3
When two species do not reproduce because of
differences in mating rituals, the situation is
referred to as
a. temporal isolation.
b. geographic isolation.
c. behavioral isolation.
d. reproductive isolation.
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16-3
All of the following played a role in speciation of
Galápagos finches EXCEPT
a. no changes in the gene pool.
b. separation of populations.
c. reproductive isolation.
d. natural selection.
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16-3
Beak size in the various groups of Galápagos
finches changed primarily in response to
a. climate.
b. mating preference.
c. food source.
d. availability of water.
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